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Ozone: Good Up High, Bad Nearby
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U.S. Nuclear Regulatory Commission
January 2003
Ozone: Good Up High, Bad Nearby
GOOD UP HIGH
What is Ozone?
Ozone is a gas that forms in the atmosphere
when 3 atoms of oxygen are combined (03). It is not emitted directly
into the air, but at ground level is created by a chemical reaction between
oxides of nitrogen (NOx), and volatile organic compounds (VOC)
in the presence of sunlight. Ozone has the same chemical structure whether
it occurs high above the earth or at ground level and can be "good" or "bad,"
depending on its location in the atmosphere.
How Can Ozone Be Both
Good and Bad?
Ozone occurs in two layers of the atmosphere.
The layer surrounding the earth's surface is the troposphere. Here, ground-level
or "bad" ozone is an air pollutant that damages human health, vegetation,
and many common materials. It is a key ingredient of urban smog. The troposphere
extends to a level about 10 miles up, where it meets the second layer, the
stratosphere. The stratospheric or "good" ozone layer extends upward from
about 10 to 30 miles and protects life on earth from the sun's harmful ultraviolet
rays (UV-b).
Too much here... Cars, trucks, power plants and factories
all emit air pollution that forms ground-level ozone or smog.
Too little there...
Many popular consumer products like air conditioners and refrigerators
involve CFCs or halons during either manufacture or use. These
chemicals damage the earth's protective oxone layer.
What is Happening to the "Good"
Ozone Layer?
Ozone occurs naturally in the stratosphere
and is produced and destroyed at a constant rate. But this "good" ozone
is gradually being destroyed by manmade chemicals called chlorofluorocarbons (CFCs),
halons, and other ozone depleting substances (used in coolants,
foaming agents, fire extinguishers, and solvents). These ozone depleting
substances degrade slowly and can remain intact for many years as they move
through the troposphere until they reach the stratosphere. There they are
broken down by the intensity of the sun's ultraviolet rays and release chlorine
and bromine molecules, which destroy "good" ozone. One chlorine or bromine
molecule can destroy 100,000 ozone molecules, causing ozone to disappear
much faster than nature can replace it.
It can take years for ozone depleting chemicals to
reach the stratosphere, and even though we have reduced or eliminated the
use of many CFCs, their impact from years past is just starting to affect
the ozone layer. Substances released into the air today will contribute to
ozone destruction well into the future.
Satellite observations indicate a world-wide thinning
of the protective ozone layer. The most noticeable losses occur over the
North and South Poles because ozone depletion accelerates in extremely cold
weather conditions.
How Does
the Depletion of "Good" Ozone Affect Human Health and the Environment?
As the stratospheric
ozone layer is depleted, higher UV-b levels reach the earth's surface. Increased
UV-b can lead to more cases of skin cancer, cataracts, and impaired immune
systems. Damage to UV-b sensitive crops, such as soybeans, reduces yield.
High altitude ozone depletion is suspected to cause decreases in phytoplankton,
a plant that grows in the ocean. Phytoplankton is an important link in the
marine food chain and, therefore, food populations could decline. Because
plants "breathe in" carbon dioxide and "breathe out" oxygen, carbon dioxide
levels in the air could also increase. Increased UV-b radiation can be instrumental
in forming more ground-level or "bad" ozone.
What is
Being Done About the Depletion of Good Ozone?
The Montreal Protocol,
a series of international agreements on the reduction and eventual elimination
of production and use of ozone depleting substances, became effective in
1989. Currently, 160 countries participate in the Protocol. Efforts will
result in recovery of the ozone layer in about 50 years.
In the United States, the U.S.
Environmental Protection Agency (EPA) continues to establish regulations
to phase out these chemicals. The Clean Air Act requires warning labels on
all products containing CFCs or similar substances, prohibits nonessential
ozone depleting products, and prohibits the release of refrigerants used
in car and home air conditioning units and appliances into the air.
BAD NEARBY
What Causes "Bad" Ozone?
Motor vehicle exhaust
and industrial emissions, gasoline vapors, and chemical solvents are some
of the major sources of NOx and VOC, also known as ozone precursors.
Strong sunlight and hot weather cause ground-level ozone to form in harmful
concentrations in the air. Many urban areas tend to have high levels of "bad"
ozone, but other areas are also subject to high ozone levels as winds carry
NOx emissions hundreds of miles away from their original sources.
Ozone concentrations can vary
from year to year. Changing weather patterns (especially the number of hot,
sunny days), periods of air stagnation, and other factors that contribute
to ozone formation make long-term predictions difficult.
How Does
"Bad" Ozone Affect Human Health and the Environment?
Repeated exposure to
ozone pollution may cause permanent damage to the lungs. Even when ozone
is present in low levels, inhaling it triggers a variety of health problems
including chest pains, coughing, nausea, throat irritation, and congestion.
It also can worsen bronchitis, heart disease, emphysema, and asthma, and
reduce lung capacity.
Healthy people also experience
difficulty in breathing when exposed to ozone pollution. Because ozone pollution
usually forms in hot weather, anyone who spends time outdoors in the summer
may be affected, particularly children, the elderly, outdoor workers and
people exercising. Millions of Americans live in areas where the national
ozone health standards are exceeded.
Ground-level ozone damages
plant life and is responsible for 500 million dollars in reduced crop production
in the United States each year. It interferes with the ability of plants
to produce and store food, making them more susceptible to disease, insects,
other pollutants, and harsh weather. "Bad" ozone damages the foliage of trees
and other plants, ruining the landscape of cities, national parks and forests,
and recreation areas.
What is
Being Done About Bad Ozone?
The Clean Air Act Amendments
of 1990 require EPA, states, and cities to implement programs to further
reduce emissions of ozone precursors from sources such as cars, fuels, industrial
facilities, power plants, and consumer/commercial products. Power plants
will be reducing emissions, cleaner cars and fuels are being developed, many
gas stations are using special nozzles at the pumps to recapture gasoline
vapors, and vehicle inspection programs are being improved to reduce emissions.
The ultimate responsibility
for our environment is our own. Minor lifestyle changes can result in major
air quality improvements.
What Can You Do?
High-Altitude "Good" Ozone
Make sure that technicians working on your car air conditioner, home
air conditioner, or refrigerator are certified by an EPA approved program
to recover the refrigerant (this is required by law).
Have your car and home air conditioner units and refrigerator checked
for leaks. When possible, repair leaky air conditioning units before refilling
them.
Contact local authorities to properly dispose of refrigeration or
air conditioning equipment.
Protect yourself against sunburn. Minimize sun exposure during midday
hours (10 am to 4 pm). Wear sunglasses, a hat with a wide brim, and protective
clothing with a tight weave. Use a broad spectrum sunscreen with a sun
protection factor (SPF) of at least 15 and 30 is better.
Ground-Level "Bad" Ozone
Keep your automobile well tuned and maintained.
Carpool, use mass transit, walk, bicycle, and/or reduce driving,
especially on hot summer days.
Be careful not to spill gasoline when filling up your car or gasoline-powered
lawn and garden equipment. During the summer, fill your gas tank during
the cooler evening hours.
Make sure your car's tires are properly inflated and your wheels are
aligned.
Participate in your local utility's energy conservation programs.
Seal containers of household cleaners, workshop chemicals and solvents,
and garden chemicals to prevent VOC from evaporating into the air. Dispose
of them properly.
We
live with ozone every day. It can protect life on earth
or harm it, but we have the power to influence
ozone's impact by the way we live.
This document is not necessarily endorsed
by the Almanac of Policy Issues. It is being preserved in the
Policy Archive for historic reasons.
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